Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductor layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
One of the important drivers for increased performance in computers is the higher levels of integration of circuits. This is accomplished by miniaturizing or shrinking device sizes on a given chip. Tolerances play an important role in being able to shrink the dimensions of a chip.
As technology nodes shrink, in some integrated circuit (IC) designs, there has been a desire to replace the typically polysilicon gate with a metal gate to improve device performance with the decreased feature sizes. One process of forming the metal gate is called a “gate last” process. In a “gate last” process, the metal gate is fabricated last, which allows for a reduced number of subsequent processes.
However, although existing “gate last” processes have been generally adequate for their intended purposes, as device scaling-down continues, they have not been entirely satisfactory in all respects.